3. B.J. Penn: Former Lightweight and Welterweight Champion

B.J. Penn (16-7-2 MMA, 12-6-2 UFC) has spent 4:33:51 fighting world class fighters at both lightweight and welterweight throughout his UFC career.

He certainly didn't rack up very much Octagon time in the beginning of his career as his first three fights lasted seven minutes and 50 seconds over three rounds.

However, out of his past 12 fights, Penn has visited Rounds 3, 4 and 5 a total of nine times.

Penn's 21 second knockout of Matt Hughes in the final bout of their trilogy and 11 second knockout of Caol Uno at UFC 34 might not of added much time to his ranking on the all-time total fight time list, but they were definitely dominant performances.